The AP4 D amplifier was designed as an extension for the AP 4.9 bit and AP 5.9 bit amplifiers, offering 4 additional 70 W amplified channels. Add this 4-channel Prima amplifier to a 4.9 bit or 5.9 bit amplifier to extend the number of channels available. When integrating with factory fitted multi-speaker systems this add on is a must for expanding the capabilities of Prima bit amplifiers. Sharing the same footprint, up to three Prima amplifiers can be stacked for maximum space efficiency without over heating. Alternatively you can use the AP 4D with a standalone processor such as Audison bit One or bit TenD. Helpful Information & Links: AP4 D User Manual AP4 D Tech Sheet Power Output: Load Impedance 4 Channels 2 Channels (Bridged) 4 Ohm 70 W x 4 260 W x 2 2 Ohm 130 W x 4